When inside your shell account, you can use the standard
psql command line utility to administer your PostgreSQL
database. Assuming your PostgreSQL database name is u777_database, you can
connect to your PostgreSQL database by issuing the following command.

psql u777_database u777_database

When asked for password, enter your database password.

Inside psql shell, you can issue SQL commands. Please see PostgreSQL
documentation for more information.